1. Field of the Invention
The present invention concerns molding optical lenses, in particular ophthalmic lenses, from a polymerizable synthetic composition.
2. Description of the Prior Art
The traditional mold comprises two pieces, typically made of mineral glasses, at the periphery of which is disposed an annular closure member, such as a gasket or an adhesive tape, defining with them the required molding cavity.
The conventional way to fill a two-piece mold as above is by causing the molding material to flow into the molding cavity through a casting opening provided for this purpose in the closure member.
In at least partly automated process, the mold to be filled is vertically aligned with a filling device adapted to deliver a particular quantity of molding material through a nozzle.
One possibility with such a vertically oriented mold is to fill the molding cavity by gravity only through a nozzle disposed on the top of the mold periphery. See for example U.S. Pat. No. 5,110,514.
Experience has shown that unless special measures are implemented, for example a relatively long waiting time (in the order of two hours, for example) between filling the mold and starting polymerization, the optical lenses obtained frequently have localized optical defects of greater or lesser severity, leading to relatively high reject rates.
To overcome the above problems, U.S. Pat. Nos. 5,547,618 and 5,662,839 propose filling the molding cavity of a two-piece mold vertically oriented through a casting opening formed in a lower part of the closure member and using pumping means adapted to cause the molding material to flow without significantly pressurizing it.
Typically filling of the molding cavity is effected using a pipe connected to a pressurized molding material reservoir and applied, like a filling nozzle, to the casting opening.
With such a method, it is possible to start polymerization immediately after filling.
However, in the case of molding material reacting at room temperature in less than 10 minutes, such as the formulation disclosed in U.S. Pat. No. 5,973,098, the pipe will clog quickly.
Using a flap valve as disclosed in U.S. Pat. No. 3,070,846 will also not be a solution since the clogging problem will still be present.
Thus, the object of the present invention is to provide a method for molding optical lenses, in particular ophthalmic lenses, from a polymerizable synthetic composition, in particular a fast curing composition, using a vertically held two-piece mold which remedies to the drawbacks of the prior art methods and molds.
A further object of the invention is to provide a method as above in which the mold is filled from the bottom.
This is achieved according to the invention by a method of making an optical lens which comprises:
filling a molding cavity vertically oriented and defined by two mold pieces at the periphery of which is disposed an annular closure member with a polymerizable synthetic composition through a disposable check valve provided in the closure member;
polymerizing the composition to form the lens; and
recovering the lens with the disposable check valve imprisoned within the polymerized composition at the periphery thereof.
The check valve is preferably provided in a bottom part of the closure member.
Preferably, the check valve is a duck bill valve. Duck bill valves are well known and commonly used for medical injection.
An embodiment of a duck bill valve is disclosed in EP 0,998,951.
Other duck bill valves are commercialized by VERNAY LABORATORIES.
The check valves, and in particular the duck bill valves, can be made of any suitable material such as aluminum, stainless steel, copper, brass, polypropylene, polytetrafluoroethylene (PTFE) and poly(tetrafluoroethylene/perfluorinated vinyl ether).
Preferably the polymerizable synthetic composition is a room temperature curing composition, and in particular a fast curing composition, i.e. a composition which cures within 10 minutes or less at room temperature. Such a composition is disclosed in U.S. Pat. No. 5,973,098.